Obama, speaking from the Rose Garden after a meeting with congressional leaders to discuss funding for the war and other issues, deplored the leak, saying he was concerned the information from the battleground "could potentially jeopardise individuals or operations".

His first public comment on the leaks came as the US army announced a criminal investigation into their source. Obama chose to play down the leaks' significance, saying: "These documents don't reveal any issues that haven't already informed our public debate on Afghanistan."

But he went on to say the material highlighted the challenges that led him to announce a change in strategy late last year that involved sending an additional 30,000 troops to Afghanistan. The policy is due to be reviewed in December.

The thousands of documents, sent to the website Wikileaks and published in the Guardian, the New York Times and Der Spiegel, dealt mainly with the conduct of the war during the Bush administration. Obama has repeatedly accused the Bush administration of ignoring the Afghanistan war because of its focus on Iraq.

"We failed for seven years to implement a strategy adequate to the challenge," Obama said today, of the period starting with the 9/11 attacks. That is why we have increased our commitment there and developed a new strategy," he said, adding he has also sent one of the finest generals in the US, General David Petraeus.

Insisting that the strategy "can work", he ended with a plea to the House of Representatives to join the Senate in passing a bill to provide funds for the Afghan war as a matter of urgency.

The leaks have focused attention on Afghanistan at a time when the Obama administration would rather concentrate on the economy – the main issue among voters – and have put pressure on him to explain why he thinks his new strategy will succeed where the old one failed. He is also facing pressure to explain continued financial, military and other support for Pakistan, despite allegations in the documents that elements in Pakistani intelligence are supporting the Taliban.

Members of Congress are becoming increasingly sceptical in public about the conduct of the war, and public support is falling. According to the latest Reuters/Ipsos, satisfaction with Obama's handling of the war has dropped to 33%, from 38% in January and 47% in February last year.

The US army is leading a criminal investigation into the source of the leak, the Pentagon said today. The army's criminal investigative command is the same body that investigated and arrested Bradley Manning, the US intelligence analyst charged earlier this month with leaking a video and other material relating to the Iraq war.

The chairman of the joint chiefs of staff, Admiral Mike Mullen, said he was appalled by the leaks, telling reporters "there is a real potential threat there to put American lives at risk."

As well as discussing the war funding bill, Afghanistan was being talked about elsewhere in Congress. The Senate foreign relations committee held a hearing on potential talks with Afghan insurgents and a Senate armed services committee held a confirmation hearing on General James Mattis, who is set to replace Petraeus as head of Centcom. Mattis, who will have overall responsibility for the US military in the Middle East and Afghanistan, was reprimanded in 2005 for saying: "You go into Afghanistan, you got guys who slap around women for five years because they didn't wear a veil. You know guys like that ain't got no manhood left anyway, so it's a hell of a lot of fun to shoot them."